Puncturing for structured low density parity check (LDPC) codes

ABSTRACT

Certain aspects of the present disclosure generally relate to techniques for puncturing of structured low density parity check (LDPC) codes. A method for wireless communications by wireless node is provided. The method generally includes encoding a set of information bits based on a LDPC code to produce a code word, the LDPC code defined by a matrix having a first number of variable nodes and a second number of check nodes, puncturing the code word to produce a punctured code word, wherein the puncturing is performed according to a first puncturing pattern designed to puncture bits corresponding to one or more of the variable nodes having a certain degree of connectivity to the check nodes, and transmitting the punctured code word.

CROSS-REFERENCE TO RELATED APPLICATION & PRIORITY CLAIM

This application claims benefit of and priority to U.S. ProvisionalPatent Application Ser. No. 62/254,678, filed Nov. 12, 2015, which isherein incorporated by reference in its entirety for all applicablepurposes.

BACKGROUND Technical Field

Certain aspects of the present disclosure generally relate to methodsand apparatus for puncturing of structured low density parity check(LDPC) codes. Certain aspects can enable improved performance tocapacity.

INTRODUCTION

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, and so on. Thesesystems may be multiple-access systems capable of supportingcommunication with multiple users by sharing the available systemresources (e.g., bandwidth and transmit power). Examples of suchmultiple-access systems include Code Division Multiple Access (CDMA)systems, Time Division Multiple Access (TDMA) systems, FrequencyDivision Multiple Access (FDMA) systems, 3^(rd) Generation PartnershipProject (3GPP) Long Term Evolution (LTE) systems, Long Term EvolutionAdvanced (LTE-A) systems, and Orthogonal Frequency Division MultipleAccess (OFDMA) systems.

Generally, a wireless multiple-access communication system cansimultaneously support communication for multiple wireless nodes. Eachnode communicates with one or more base stations via transmissions onforward and reverse links. The forward link (or downlink) refers to acommunication link from base stations to nodes, and a reverse link (oruplink) refers to a communication link from nodes to base stations.Communication links may be established via a single-input single-output,multiple-input single-output, or a multiple-input multiple-output (MIMO)system.

In the modern information age, binary values (e.g., ones and zeros), areused to represent and communicate various types of information, such asvideo, audio, statistical information, etc. Unfortunately, duringstorage, transmission, and/or processing of binary data, errors may beunintentionally introduced; for example, a one may be changed to a zeroor vice versa.

Generally, in the case of data transmission, a receiver observes eachreceived bit in the presence of noise or distortion and only anindication of the bit's value is obtained. Under these circumstances,the observed values are interpreted as a source of “soft” bits. A softbit indicates a preferred estimate of the bit's value (e.g., a one or azero) together with some indication of the reliability of that estimate.While the number of errors may be relatively low, even a small number oferrors or level of distortion can result in the data being unusable or,in the case of transmission errors, may necessitate retransmission ofthe data.

In order to provide a mechanism to check for errors and, in some cases,to correct errors, binary data can be coded to introduce carefullydesigned redundancy. Coding of a unit of data produces what is commonlyreferred to as a code word. Because of its redundancy, a code word willoften include more bits than the input unit of data from which the codeword was produced.

Redundant bits are added by an encoder to the transmitted bit stream tocreate a code word. When signals arising from transmitted code words arereceived or processed, the redundant information included in the codeword as observed in the signal can be used to identify and/or correcterrors in or remove distortion from the received signal in order torecover the original data unit. Such error checking and/or correctingcan be implemented as part of a decoding process. In the absence oferrors, or in the case of correctable errors or distortion, decoding canbe used to recover from the source data being processed, the originaldata unit that was encoded. In the case of unrecoverable errors, thedecoding process may produce some indication that the original datacannot be fully recovered. Such indications of decoding failure can beused to initiate retransmission of the data.

With the increased use of fiber optic lines for data communication andincreases in the rate at which data can be read from and stored to datastorage devices, (e.g., disk drives, tapes, etc.), there is anincreasing need not only for efficient use of data storage andtransmission capacity but also for the ability to encode and decode dataat high rates of speed.

While encoding efficiency and high data rates are important, for anencoding and/or decoding system to be practical for use in a wide rangeof devices (e.g., consumer devices), it is important that the encodersand/or decoders be capable of being implemented at reasonable cost.

Communication systems often need to operate at several different rates.One way to keep the implementation as simple as possible and to providefor the coding and decoding at the different rates is to uselow-density-parity check (LDPC) codes. In particular, the LDPC codes areused to generate higher-rate codes by puncturing lower-rate codes.Techniques for improved performance of LDPC codes are desirable.

BRIEF SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims which follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include improvedcommunications between access points and stations in a wireless network.

Certain aspects of the present disclosure generally relate to methodsand apparatus for puncturing of structured low density parity check(LDPC) codes. In some scenarios, highest degree variable nodes of a 5/6code rate Wi-Fi LDPC code (e.g., an LDPC code defined by the 802.11wireless standard) can be punctured to provide a 7/8 code rate for theLDPC code. In some scenarios, a multi-edge LDPC code design having anextra variable node can be punctured to provide a 7/8 code rate LDPCcode.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a transmitting device. The method generally includesencoding a set of information bits based on a LDPC code to produce acode word, the LDPC code defined by a matrix having a first number ofvariable nodes and a second number of check nodes, puncturing the codeword to produce a punctured code word, wherein the puncturing isperformed according to a first puncturing pattern designed to puncturebits corresponding to one or more of the variable nodes having a certaindegree of connectivity to the check nodes, and transmitting thepunctured code word.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a transmitting device. The method generally includesencoding a set of information bits based on a multi-edge LDPC code toproduce a code word, the LDPC code defined by a matrix having a firstnumber of variable nodes including an extra variable node, relative to areference LDPC code, and a second number of check nodes; puncturing thecode word to produce a punctured code word, wherein the puncturing isperformed according to a \puncturing pattern designed to puncture bitscorresponding to one or more of the variable nodes to achieve a certaincode rate for the punctured code word; and transmitting the puncturedcode word.

Certain aspects of the present disclosure provide an apparatus forwireless communications such as a transmitting device. The apparatusgenerally includes means for encoding a set of information bits based ona LDPC code to produce a code word, the LDPC code defined by a matrixhaving a first number of variable nodes and a second number of checknodes, means for puncturing the code word to produce a punctured codeword, wherein the puncturing is performed according to a firstpuncturing pattern designed to puncture bits corresponding to one ormore of the variable nodes having a certain degree of connectivity tothe check nodes, and means for transmitting the punctured code word.

Certain aspects of the present disclosure provide an apparatus forwireless communications such as a transmitting device. The apparatusgenerally includes means for encoding a set of information bits based ona multi-edge LDPC code to produce a code word, the LDPC code defined bya matrix having a first number of variable nodes including an extravariable node, relative to a reference LDPC code, and a second number ofcheck nodes; means for puncturing the code word to produce a puncturedcode word, wherein the puncturing is performed according to a puncturingpattern designed to puncture bits corresponding to one or more of thevariable nodes to achieve a certain code rate for the punctured codeword; and means for transmitting the punctured code word.

Certain aspects of the present disclosure provide an apparatus forwireless communications such as a transmitting device. The apparatusgenerally includes at least one processor configured to encode a set ofinformation bits based on a LDPC code to produce a code word, the LDPCcode defined by a matrix having a first number of variable nodes and asecond number of check nodes and puncture the code word to produce apunctured code word, wherein the puncturing is performed according to afirst puncturing pattern designed to puncture bits corresponding to oneor more of the variable nodes having a certain degree of connectivity tothe check nodes; and a transmitter configured to transmit the puncturedcode word.

Certain aspects of the present disclosure provide an apparatus forwireless communications such as a transmitting device. The apparatusgenerally includes at least one processor configured to encode a set ofinformation bits based on a multi-edge LDPC code to produce a code word,the LDPC code defined by a matrix having a first number of variablenodes including an extra variable node, relative to a reference LDPCcode, and a second number of check nodes and puncture the code word toproduce a punctured code word, wherein the puncturing is performedaccording to a puncturing pattern designed to puncture bitscorresponding to one or more of the variable nodes to achieve a certaincode rate for the punctured code word; and a transmitter configured totransmit the punctured code word.

Certain aspects of the present disclosure provide a computer readablemedium having computer executable code stored thereon. The computerexecutable code generally includes code for encoding a set ofinformation bits based on a LDPC code to produce a code word, the LDPCcode defined by a matrix having a first number of variable nodes and asecond number of check nodes, code for puncturing the code word toproduce a punctured code word, wherein the puncturing is performedaccording to a first puncturing pattern designed to puncture bitscorresponding to one or more of the variable nodes having a certaindegree of connectivity to the check nodes, and code for transmitting thepunctured code word.

Certain aspects of the present disclosure provide a computer readablemedium having computer executable code stored thereon. The computerexecutable code generally includes code for encoding a set ofinformation bits based on a multi-edge LDPC code to produce a code word,the LDPC code defined by a matrix having a first number of variablenodes including an extra variable node, relative to a reference LDPCcode, and a second number of check nodes, code for puncturing the codeword to produce a punctured code word, wherein the puncturing isperformed according to a puncturing pattern designed to puncture bitscorresponding to one or more of the variable nodes to achieve a certaincode rate for the punctured code word; and code for transmitting thepunctured code word.

Other aspects, features, and embodiments of the present invention willbecome apparent to those of ordinary skill in the art, upon reviewingthe following description of specific, exemplary embodiments of thepresent invention in conjunction with the accompanying figures. Whilefeatures of the present invention may be discussed relative to certainembodiments and figures below, all embodiments of the present inventioncan include one or more of the advantageous features discussed herein.In other words, while one or more embodiments may be discussed as havingcertain advantageous features, one or more of such features may also beused in accordance with the various embodiments of the inventiondiscussed herein. In similar fashion, while exemplary embodiments may bediscussed below as device, system, or method embodiments it should beunderstood that such exemplary embodiments can be implemented in variousdevices, systems, and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the appended drawings. The appended drawingsillustrate only certain typical aspects of this disclosure, however, andare therefore not to be considered limiting of its scope, for thedescription may admit to other equally effective aspects.

FIG. 1 illustrates an example multiple access wireless communicationsystem, in accordance with certain aspects of the present disclosure.

FIG. 2 illustrates a block diagram of a base station and a wirelessnode, in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice, in accordance with certain aspects of the present disclosure.

FIGS. 4-4A show graphical and matrix representations of an exemplary lowdensity parity check (LDPC) code, in accordance with certain aspects ofthe present disclosure.

FIG. 5 graphically illustrates lifting of the LDPC code of FIG. 4A, inaccordance with certain aspects of the present disclosure.

FIG. 6 is a simplified block diagram illustrating a puncturing encoder,in accordance with certain aspects of the present disclosure.

FIG. 7 is a simplified block diagram illustrating a decoder, inaccordance with certain aspects of the present disclosure.

FIG. 8 is a flow diagram illustrating example operations for encodinginformation based on puncturing of highest degree nodes in an LDPC codestructure for wireless communications by a transmitting device, inaccordance with certain aspects of the present disclosure.

FIG. 9 shows a base graph representation of an exemplary 5/6 rate Wi-FiLDPC code.

FIG. 10 shows a graphical representation of the exemplary 5/6 rate Wi-FiLDPC code shown in FIG. 9 having a punctured low degree variable node.

FIG. 11 shows a graphical representation of the exemplary 5/6 rate Wi-FiLDPC code shown in FIG. 9 having a punctured highest degree variablenode, in accordance with certain aspects of the present disclosure.

FIG. 12 is a graph showing performance of various puncturing techniquesof an LDPC code at modulation and coding scheme (MCS) 9, in accordancewith certain aspects of the present disclosure.

FIG. 13 is a graph showing performance of various puncturing techniquesof an LDPC code at MCS 1, in accordance with certain aspects of thepresent disclosure.

FIG. 14 is a flow diagram illustrating example operations for encodinginformation based on an LDPC code structure for wireless communicationsby a transmitting device, in accordance with certain aspects of thepresent disclosure.

FIG. 15 is a matrix representation of an example multi-edge 7/8 rateLDPC code design, in accordance with certain aspects of the presentdisclosure.

FIG. 16 is a matrix representation of another example multi-edge rate7/8 LDPC code design, in accordance with certain aspects of the presentdisclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques for puncturing oflow density parity check (LDPC) codes. In some scenarios, highest degreevariable nodes of a 5/6 code rate Wi-Fi LDPC code (e.g., an LDPC codedefined by the 802.11 wireless standard) can be punctured to provide a7/8 code rate for the LDPC code. In some scenarios, a multi-edge LDPCcode having an extra variable node can be punctured to provide a 7/8code rate for the LDPC code and maintaining a desired block length.

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosuredisclosed herein, whether implemented independently of or combined withany other aspect of the disclosure. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim. The word “exemplary”is used herein to mean “serving as an example, instance, orillustration.” Any aspect described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otheraspects.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

The techniques described herein may be used for various wirelesscommunication networks such as Code Division Multiple Access (CDMA)networks, Time Division Multiple Access (TDMA) networks, FrequencyDivision Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA)networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms“networks” and “systems” are often used interchangeably. A CDMA networkmay implement a radio technology such as Universal Terrestrial RadioAccess (UTRA), CDMA2000, etc. UTRA includes Wideband-CDMA (W-CDMA) andLow Chip Rate (LCR). CDMA2000 covers IS-2000, IS-95, and IS-856standards. A TDMA network may implement a radio technology such asGlobal System for Mobile Communications (GSM). An OFDMA network mayimplement a radio technology such as Evolved UTRA (E-UTRA), IEEE 802.11,IEEE 802.16, IEEE 802.20, Flash-OFDM®, etc. UTRA, E-UTRA, and GSM arepart of Universal Mobile Telecommunication System (UMTS). Long TermEvolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA,GSM, UMTS, and LTE are described in documents from an organization named“3rd Generation Partnership Project” (3GPP). CDMA2000 is described indocuments from an organization named “3rd Generation Partnership Project2” (3GPP2). These communications networks are merely listed as examplesof networks in which the techniques described in this disclosure may beapplied; however, this disclosure is not limited to the above-describedcommunications network.

Single carrier frequency division multiple access (SC-FDMA) is atransmission technique that utilizes single carrier modulation at atransmitter side and frequency domain equalization at a receiver side.The SC-FDMA has similar performance and essentially the same overallcomplexity as those of OFDMA system. However, SC-FDMA signal has lowerpeak-to-average power ratio (PAPR) because of its inherent singlecarrier structure. The SC-FDMA has drawn great attention, especially inthe uplink (UL) communications where lower PAPR greatly benefits thewireless node in terms of transmit power efficiency.

An access point (“AP”) may comprise, be implemented as, or known asNodeB, Radio Network Controller (“RNC”), eNodeB (eNB), Base StationController (“BSC”), Base Transceiver Station (“BTS”), Base Station(“BS”), Transceiver Function (“TF”), Radio Router, Radio Transceiver,Basic Service Set (“BSS”), Extended Service Set (“ESS”), Radio BaseStation (“RBS”), or some other terminology.

An access terminal (“AT”) may comprise, be implemented as, or be knownas an access terminal, a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, user equipment (UE), a user station, a wirelessnode, or some other terminology. In some implementations, an accessterminal may comprise a cellular telephone, a smart phone, a cordlesstelephone, a Session Initiation Protocol (“SIP”) phone, a wireless localloop (“WLL”) station, a personal digital assistant (“PDA”), a tablet, anetbook, a smartbook, an ultrabook, a handheld device having wirelessconnection capability, a Station (“STA”), or some other suitableprocessing device connected to a wireless modem. Accordingly, one ormore aspects taught herein may be incorporated into a phone (e.g., acellular phone, a smart phone), a computer (e.g., a desktop), a portablecommunication device, a portable computing device (e.g., a laptop, apersonal data assistant, a tablet, a netbook, a smartbook, anultrabook), medical devices or equipment, biometric sensors/devices, anentertainment device (e.g., a music or video device, or a satelliteradio), a vehicular component or sensor, smart meters/sensors,industrial manufacturing equipment, a global positioning system device,or any other suitable device that is configured to communicate via awireless or wired medium. In some aspects, the node is a wireless node.A wireless node may provide, for example, connectivity for or to anetwork (e.g., a wide area network such as the Internet or a cellularnetwork) via a wired or wireless communication link.

It is noted that while aspects may be described herein using terminologycommonly associated with 3G and/or 4G wireless technologies, aspects ofthe present disclosure can be applied in other generation-basedcommunication systems, such as 5G and later.

An Example Wireless Communication System

FIG. 1 illustrates an example communications network 100 in whichaspects of the present disclosure may be performed. For example, atransmitting device such as wireless node 116 or BS 102 can encode a setof information bits based on a low density parity check (LDPC) code toproduce a code word, the LDPC code defined by a matrix having a firstnumber of variable nodes and a second number of check nodes. Thetransmitting device can puncture the code word to produce a puncturedcode word. For example, the transmitting device can performed thepuncturing according to a puncturing pattern. The transmitting devicemay puncture bits corresponding to one or more of the variable nodeshaving a certain degree of connectivity to the check nodes (e.g., ahighest degree of connectivity). The transmitting device can thentransmit the punctured code word.

Referring to FIG. 1, a multiple access wireless communication system 100according to one aspect is illustrated. A base station (BS) 102 mayinclude multiple antenna groups, one group including antennas 104 and106, another group including antennas 108 and 110, and an additionalgroup including antennas 112 and 114. In FIG. 1, only two antennas areshown for each antenna group, however, more or fewer antennas may beutilized for each antenna group. Wireless node 116 may be incommunication with antennas 112 and 114, where antennas 112 and 114transmit information to wireless node 116 over forward link 120 andreceive information from wireless node 116 over reverse link 118.Wireless node 122 may be in communication with antennas 106 and 108,where antennas 106 and 108 transmit information to wireless node 122over forward link 126 and receive information from wireless node 122over reverse link 124. The BS 102 may also be in communication withother wireless nodes, which may be, for example, Internet-of-Everything(IoE) devices. IoE device 136 may be in communication with one or moreother antennas of BS 102, where the antennas transmit information to IoEdevice 136 over forward link 140 and receive information from IoE device136 over reverse link 138. IoE device 142 may be in communication withone or more other antennas of BS 102, where the antennas transmitinformation to IoE device 142 over forward link 146 and receiveinformation from IoE device 142 over reverse link 144. In a FrequencyDivision Duplex (FDD) system, communication links 118, 120, 124, 126,138, 140, 144, and 146 may use different frequency for communication.For example, forward link 120 may use a different frequency than thatused by reverse link 118, and forward link 140 may use a differentfrequency than that used by reverse link 138.

Each group of antennas and/or the area in which they are designed tocommunicate is often referred to as a sector of the BS. In one aspect ofthe present disclosure, each antenna group may be designed tocommunicate to wireless nodes in a sector of the areas covered by accesspoint 102.

Wireless node 130 may be in communication with BS 102, where antennasfrom the BS 102 transmit information to wireless node 130 over forwardlink 132 and receive information from the wireless node 130 over reverselink 134.

In communication over forward links 120 and 126, the transmittingantennas of BS 102 may utilize beamforming in order to improve thesignal-to-noise ratio of forward links for the different wireless nodes116, 122, 136, and 142. Also, a BS using beamforming to transmit towireless nodes scattered randomly through its coverage causes lessinterference to wireless nodes in neighboring cells than a BStransmitting through a single antenna to all its wireless nodes.

FIG. 2 illustrates a block diagram of an aspect of a transmitter system210 (e.g., also known as the base station) and a receiver system 250(e.g., also known as the wireless node) in a multiple-inputmultiple-output (MIMO) system 200. Each of system 210 and system 250 hascapabilities to both transmit and receive. Whether system 210 or system250 is transmitting, receiving, or transmitting and receivingsimultaneously depends on the application. At the transmitter system210, traffic data for a number of data streams is provided from a datasource 212 to a transmit (TX) data processor 214.

In one aspect of the present disclosure, each data stream may betransmitted over a respective transmit antenna. TX data processor 214formats, codes, and interleaves the traffic data for each data streambased on a particular coding scheme selected for that data stream toprovide coded data. According to aspects described herein, the codingscheme may use LDPC codes.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (e.g., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QSPK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by processor 230. Memory 232 may store data andsoftware/firmware for the transmitter system 210.

The modulation symbols for all data streams are then provided to a TXMIMO processor 220, which may further process the modulation symbols(e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulationsymbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. Incertain aspects of the present disclosure, TX MIMO processor 220 appliesbeamforming weights to the symbols of the data streams and to theantenna from which the symbol is being transmitted.

Each transmitter 222 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transmitters 222 a through 222 t are thentransmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals may bereceived by N_(R) antennas 252 a through 252 r and the received signalfrom each antenna 252 may be provided to a respective receiver (RCVR)254 a through 254 r. Each receiver 254 may condition (e.g., filters,amplifies, and downconverts) a respective received signal, digitize theconditioned signal to provide samples, and further process the samplesto provide a corresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) receivedsymbol streams from N_(R) receivers 254 based on a particular receiverprocessing technique to provide N_(T) “detected” symbol streams. The RXdata processor 260 then demodulates, deinterleaves, and decodes eachdetected symbol stream to recover the traffic data for the data stream.The processing by RX data processor 260 may be complementary to thatperformed by TX MIMO processor 220 and TX data processor 214 attransmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use.Processor 270 formulates a reverse link message comprising a matrixindex portion and a rank value portion. Memory 272 may store data andsoftware/firmware for the receiver system 250. The reverse link messagemay comprise various types of information regarding the communicationlink and/or the received data stream. The reverse link message is thenprocessed by a TX data processor 238, which also receives traffic datafor a number of data streams from a data source 236, modulated by amodulator 280, conditioned by transmitters 254 a through 254 r, andtransmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system250 are received by antennas 224, conditioned by receivers 222,demodulated by a demodulator 240, and processed by a RX data processor242 to extract the reserve link message transmitted by the receiversystem 250. Processor 230 then determines which pre-coding matrix to usefor determining the beamforming weights, and then processes theextracted message.

Any one of the processor 270, RX data processor 260, TX data processor238, or other processors/elements, or a combination thereof of thewireless node 250 and/or any one of the processor 230, TX MIMO processor220, TX data processor 214, RX data processor 242, or otherprocessors/elements, or a combination thereof of the access point 210may be configured to perform the procedures for connectionless access inaccordance with certain aspects of the present disclosure discussedbelow. In an aspect, at least one of the processor 270, RX dataprocessor 260, and TX data processor 238 may be configured to executealgorithms stored in memory 272 for performing the random-access channel(RACH) procedures for connectionless access described herein. In anotheraspect, at least one of the processor 230, TX MIMO processor 220, TXdata processor 214, and RX data processor 242 may be configured toexecute algorithms stored in memory 232 for performing the RACHprocedures for connectionless access described herein.

FIG. 3 illustrates various components that may be utilized in a wirelessdevice 302 that may be employed within the wireless communication system100 illustrated in FIG. 1. The wireless device 302 is an example of adevice that may be configured to implement the various methods describedherein. The wireless device 302 may be a base station 102 or any of thewireless nodes (e.g., 116, 122, 136, and 142). For example, the wirelessdevice 302 may be configured to perform operations 800 described in FIG.8 (as well as other operations described herein).

The wireless device 302 may include a processor 304 that controlsoperation of the wireless device 302. The processor 304 may also bereferred to as a central processing unit (CPU). Memory 306, which mayinclude both read-only memory (ROM) and random access memory (RAM),provides instructions and data to the processor 304. A portion of thememory 306 may also include non-volatile random access memory (NVRAM).The processor 304 typically performs logical and arithmetic operationsbased on program instructions stored within the memory 306. Theinstructions in the memory 306 may be executable to implement themethods described herein, for example, to allow a UE to transmit dataefficiently during a connectionless access. Some non-limiting examplesof the processor 304 may include Snapdragon processor, applicationspecific integrated circuits (ASICs), programmable logic, etc.

The wireless device 302 may also include a housing 308 that may includea transmitter 310 and a receiver 312 to allow transmission and receptionof data between the wireless device 302 and a remote location. Thetransmitter 310 and receiver 312 may be combined into a transceiver 314.A single or a plurality of transmit antennas 316 may be attached to thehousing 308 and electrically coupled to the transceiver 314. Thewireless device 302 may also include (not shown) multiple transmitters,multiple receivers, and multiple transceivers. The wireless device 302can also include wireless battery charging equipment.

The wireless device 302 may also include a signal detector 318 that maybe used in an effort to detect and quantify the level of signalsreceived by the transceiver 314. The signal detector 318 may detect suchsignals as total energy, energy per subcarrier per symbol, powerspectral density and other signals. The wireless device 302 may alsoinclude a digital signal processor (DSP) 320 for use in processingsignals.

The various components of the wireless device 302 may be coupledtogether by a bus system 322, which may include a power bus, a controlsignal bus, and a status signal bus in addition to a data bus. Theprocessor 304 may be configured to access instructions stored in thememory 306 to perform connectionless access, in accordance with aspectsof the present disclosure discussed below.

Example Error Correction Coding

Many communications systems use error-correcting codes. Specifically,error correcting codes compensate for the intrinsic unreliability ofinformation transfer in these systems by introducing redundancy into thedata stream. Low density parity check (LDPC) codes (also known asGallager codes) are a particular type of error correcting codes whichuse an iterative coding system. LDPC codes are linear block code inwhich most of the elements of its parity check matrix H are ‘0’.

LDPC codes can be represented by bipartite graphs (often referred to as“Tanner graphs”), wherein a set of variable nodes corresponds to bits ofa code word (e.g., information bits or systematic bits), and a set ofcheck nodes correspond to a set of parity-check constraints that definethe code. Thus, the nodes of the graph are separated into twodistinctive sets and with edges connecting nodes of two different types,variable and check.

A protograph is created by copying a bipartite base graph (G) a numberof times, N. A variable node and a check node are considered “neighbors”if they are connected by an “edge” (i.e., the line connecting thevariable node and the check node) in the graph. In addition, for eachedge (e) of the bipartite base graph (G), a permutation is applied tothe N copies of edge (e) to interconnect the N copies of G. A bitsequence having a one-to-one association with the variable node sequenceis a valid code word if and only if, for each check node, the bitsassociated with all neighboring variable nodes sum to zero modulo two(i.e., they include an even number of 1's). The resulting LDPC code maybe quasi-cyclic (QC) if the permutations used are cyclic.

FIGS. 4-4A show graphical and matrix representations of an exemplaryLDPC code, in accordance with certain aspects of the present disclosure.For example, FIG. 4 shows a bipartite graph 400 representing anexemplary LDPC code. The bipartite graph 400 includes a set of 5variable nodes 410 (represented by circles) connected to 4 check nodes420 (represented by squares). Edges in the graph 400 connect variablenodes 410 to the check nodes 420 (represented by the lines connectingthe variable nodes 410 to the check nodes 420). This graph consists of|V|=5 variable nodes and |C|=4 check nodes, connected by |E|=12 edges.

The bipartite graph may be represented by a simplified adjacency matrix.FIG. 4A shows a matrix representation 400A of the bipartite graph 400.The matrix representation 400A includes a parity check matrix H and acode word vector x, where x₁-x₅ represent bits of the code word x. Theparity matrix H is used for determining whether a received signal wasnormally decoded. The parity check matrix H has C rows corresponding toj check nodes and V columns corresponding to i variable nodes (i.e., ademodulated symbol), where the rows represent the equations and thecolumns represents the bits of the code word. In FIG. 4A, matrix H has 4rows and 5 columns corresponding to 4 check nodes and 5 variable nodesrespectfully. If a j-th check node is connected to an i-th variable nodeby an edge, i.e., the two nodes are neighbors, then there is a 1 in thei-th column and in the j-th row of the parity check matrix H. That is,the intersection of an i-th row and a j-th column contains a “1” wherean edge joins the corresponding vertices and a “0” where there is noedge. The code word vector x represents a valid code word if and only ifH_(x)=0 (e.g., if, for each constraint node, the bits neighboring theconstraint (via their association with variable nodes) sum to zeromodulo two, i.e., they comprise an even number of ones). Thus, if thecode word is received correctly, then H_(x)=0 (mod 2). When the productof a coded received signal and the parity check matrix H becomes ‘0’,this signifies that no error has occurred. The parity check matrix is aC row by V column binary matrix. The rows represent the equations andthe columns represent the digits in the code word.

The number of demodulated symbols or variable nodes is the LDPC codelength. The number of non-zero elements in a row (column) is defined asthe row (column) weight d_(c)(d_(v)).

The degree of a node refers to the number of edges connected to thatnode. This feature is illustrated in the H matrix shown in FIG. 4A wherethe number of edges incident to a variable node 410 is equal to thenumber of 1's in the corresponding column and is called the variablenode degree d(v). Similarly, the number of edges connected with a checknode 420 is equal to the number of ones in a corresponding row and iscalled the check node degree d(c).

A regular graph or code is one for which all variable nodes have thesame degree and all constraint nodes have the same degree. In this case,we say that the code is a regular code. On the other hand, an irregularcode has constraint nodes and/or variable nodes of differing degrees.For example, some variable nodes may be of degree 4, others of degree 3and still others of degree 2.

“Lifting” enables LDPC codes to be implemented using parallel encodingand/or decoding implementations while also reducing the complexitytypically associated with large LDPC codes. More specifically, liftingis a technique for generating a relatively large LDPC code from multiplecopies of a smaller base code. For example, a lifted LDPC code may begenerated by producing a number (Z) of parallel copies of the base graphand then interconnecting the parallel copies through permutations ofedge clusters of each copy of the base graph.

Thus, a larger graph can be obtained by a “copy and permute” operationwhere multiple copies are overlaid so that same-type vertices are inclose proximity, but the overall graph consists of multiple disconnectedsubgraphs.

FIG. 5 graphically illustrates the effect of making three copies of thegraph of FIG. 4. Three copies may be interconnected by permuting likeedges among the copies. If the permutations are restricted to cyclicpermutations, then the resulting graph corresponds to a quasi-cyclicLDPC with lifting Z=3. The original graph from which three copies weremade is referred to herein as the base graph. To obtain derived graphsof different sizes, we can apply the “copy and permute” operation to abase graph.

A received LDPC code word can be decoded to produce a reconstructedversion of the original code word. In the absence of errors, or in thecase of correctable errors, decoding can be used to recover the originaldata unit that was encoded. Redundant bits may be used by decoders todetect and correct bit errors. LDPC decoder(s) generally operate byiteratively performing local calculations and passing those results byexchanging messages within the bipartite graph 400, along the edges, andupdating these messages by performing computations at the nodes based onthe incoming messages. These steps may typically be repeated severaltimes. For example, each variable node 410 in the graph 400 mayinitially be provided with a “soft bit” (e.g., representing the receivedbit of the code word) that indicates an estimate of the associated bit'svalue as determined by observations from the communications channel.Using these soft bits the LDPC decoders may update messages byiteratively reading them, or some portion thereof, from memory andwriting an updated message, or some portion thereof, back to, memory.The update operations are typically based on the parity checkconstraints of the corresponding LDPC code. In implementations forlifted LDPC codes, messages on like edges are often processed inparallel.

LDPC codes designed for high speed applications often use quasi-cyclicconstructions with large lifting factors and relatively small basegraphs to support high parallelism in encoding and decoding operations.LDPC codes with higher code rates (e.g., the ratio of the message lengthto the code word length) tend to have relatively fewer parity checks. Ifthe number of base parity checks is smaller than the degree of avariable node (e.g., the number of edges connected to a variable node),then, in the base graph, that variable node is connected to at least oneof the base parity checks by two or more edges (e.g., the variable nodemay have a “double edge”). Or if the number of base parity checks issmaller than the degree of a variable node (e.g., the number of edgesconnected to a variable node), then, in the base graph, that variablenode is connected to at least one of the base parity checks by two ormore edges. Having a base variable node and a base check node connectedby two or more edges is generally undesirable for parallel hardwareimplementation purposes. For example, such double edges may result inmultiple concurrent read and write operations to the same memorylocations, which in turn may create data coherency problems. A doubleedge in a base LDPC code may trigger parallel reading of the same softbit value memory location twice during a single parallel parity checkupdate. Thus, additional circuitry is typically needed to combine thesoft bit values that are written back to memory, so as to properlyincorporate both updates. However, eliminating double edges in the LDPCcode helps to avoid this extra complexity.

LDPC code designs based on cyclic lifting can be interpreted as codesover the ring of polynomials modulo may be binary polynomials modulox^(z)−1, where Z is the lifting size (e.g., the size of the cycle in thequasi-cyclic code). Thus encoding such codes can often be interpreted asan algebraic operation in this ring.

In the definition of standard irregular LDPC code ensembles (degreedistributions) all edges in the Tanner graph representation may bestatistically interchangeable. In other words, there exists a singlestatistical equivalence class of edges. For multi-edge LDPC codes,multiple equivalence classes of edges may be possible. While in thestandard irregular LDPC ensemble definition, nodes in the graph (bothvariable and constraint) are specified by their degree, i.e., the numberof edges they are connected to, in the multi-edge type setting an edgedegree is a vector; it specifies the number of edges connected to thenode from each edge equivalence class (type) independently. A multi-edgetype ensemble is comprised of a finite number of edge types. The degreetype of a constraint node is a vector of (non-negative) integers; thei-th entry of this vector records the number of sockets of the i-th typeconnected to such a node. This vector may be referred to as an edgedegree. The degree type of a variable node has two parts although it canbe viewed as a vector of (non-negative) integers. The first part relatesto the received distribution and will be termed the received degree andthe second part specifies the edge degree. The edge degree plays thesame role as for constraint nodes. Edges are typed as they pair socketsof the same type. This constraint, that sockets must pair with socketsof like type, characterizes the multi-edge type concept. In a multi-edgetype description, different node types can have different receiveddistributions (e.g., the associated bits may go through differentchannels).

Puncturing is the act of removing bits from a code word to yield ashorter code word. Thus, punctured variable nodes correspond to codeword bits that are not actually transmitted. Puncturing a variable nodein an LDPC code creates a shortened code (e.g. due to the removal of abit), while also effectively removing a check node. Specifically, for amatrix representation of an LDPC code, including bits to be punctured,where the variable node to be punctured has a degree of one (such arepresentation may be possible through row combining provided the codeis proper), puncturing the variable node removes the associated bit fromthe code and effectively removes its single neighboring check node fromthe graph. As a result, the number of check nodes in the graph isreduced by one.

FIG. 6 is a simplified block diagram illustrating a puncturing encoder,in accordance with certain aspects of the present disclosure. FIG. 6 isa simplified block diagram 600 illustrating a portion of a radiofrequency (RF) modem 650 that may be configured to provide a signalincluding a punctured encoded message for wireless transmission. In oneexample, a convolutional encoder 602 in a base station 102 (or an accessterminal on the reverse path) receives a message 620 for transmission.The message 620 may contain data and/or encoded voice or other contentdirected to the receiving device. The encoder 602 encodes the messageusing a suitable modulation and coding scheme (MCS), typically selectedbased on a configuration defined by the base station 102 or anothernetwork entity. An encoded bit stream 622 produced by the encoder 602may then be selectively punctured by a puncturing module 604, which maybe a separate device or component, or which may be integrated with theencoder 602. The puncturing module 604 may determine that the bit streamshould be punctured prior to transmission, or transmitted withoutpuncturing. The decision to puncture the bit stream 622 is typicallymade based on network conditions, network configuration, RAN definedpreferences and/or for other reasons. The bit stream 622 may bepunctured according to a puncture pattern 612 and used to encode themessage 620. The puncturing pattern may be according to certain aspectdescribed in more detail below. The puncturing module 604 provides anoutput 624 to a mapper 606 that generates a sequence of Tx symbols 626that are modulated, amplified and otherwise processed by Tx chain 608 toproduce an RF signal 628 for transmission through antenna 610.

The output 624 of the puncturing module 604 may be the unpunctured bitstream 622 or a punctured version of the bit stream 622, according towhether the modem portion 650 is configured to puncture the bit stream622. In one example, parity and/or other error correction bits may bepunctured in the output 624 of the encoder 602 in order to transmit themessage 620 within a limited bandwidth of the RF channel. In anotherexample, the bit stream may be punctured to reduce the power needed totransmit the message 620, to avoid interference, or for othernetwork-related reasons. These punctured code word bits are nottransmitted.

The decoders and decoding algorithms used to decode LDPC code wordsoperate by exchanging messages within the graph along the edges andupdating these messages by performing computations at the nodes based onthe incoming messages. Each variable node in the graph is initiallyprovided with a soft bit, termed a received value, that indicates anestimate of the associated bit's value as determined by observationsfrom, e.g., the communications channel. Ideally, the estimates forseparate bits are statistically independent. This ideal may be violatedin practice. A received word is comprised of a collection of receivedvalues.

FIG. 7 is a simplified block diagram illustrating a decoder, inaccordance with certain aspects of the present disclosure. FIG. 7 is asimplified schematic 700 illustrating a portion of a RF modem 750 thatmay be configured to receive and decode a wirelessly transmitted signalincluding a punctured encoded message. The punctured code word bits maybe treated as erased. For example, the LLRs of the punctured nodes maybe set to zero at initialization. In various examples, the modem 750receiving the signal may reside at the access terminal, at the basestation, or at any other suitable apparatus or means for carrying outthe described functions. An antenna 702 provides an RF signal 720 to anaccess terminal. An RF chain 704 processes and demodulates the RF signal720 and may provide a sequence of symbols 722 to a demapper 706, whichproduces a bit stream 724 representative of the encoded message.

The demapper 706 may provide a depunctured bit stream 724. In oneexample, the demapper 706 may include a depuncturing module that can beconfigured to insert null values at locations in the bit stream at whichpunctured bits were deleted by the transmitter. The depuncturing modulemay be used when the puncture pattern 710 used to produce the puncturedbit stream at the transmitter is known. According to certain aspectsdisclosed herein, the puncture pattern 710 can be used to identifylog-likelihood ratios (LLRs) 728 that may be ignored during decoding ofthe bit stream 724 by the convolutional decoder 708. The LLRs may beassociated with a set of depunctured bit locations in the bit stream724. Accordingly, the decoder 708 may produce the decoded message 726with reduced processing overhead by ignoring the identified LLRs 728.For some aspects, the LDPC decoder may include a plurality of processingelements to perform the parity check or variable node operations inparallel. For example, when processing a code word with lifting size Z,the LDPC decoder may utilize a number (Z) of processing elements toperform parity check operations on all Z edges of a lifted graph,concurrently.

According to certain aspects disclosed herein, processing efficiency ofa decoder 708 may be improved by configuring the decoder 708 to ignoreLLRs 728 that correspond to punctured bits in a message transmitted in apunctured bit stream 722. The punctured bit stream 722 may have beenpunctured according to a puncturing scheme that defines certain bits tobe removed from an encoded message. In one example, certain parity orother error-correction bits may be removed. A puncturing pattern may beexpressed in a puncturing matrix or table that identifies the locationof bits to be punctured in each message. A puncturing scheme may beselected to reduce processing overhead used to decode the message 726while maintaining compliance with data rates on the communicationchannel and/or with transmission power limitations set by the network. Aresultant punctured bit stream typically exhibits the error-correctingcharacteristics of a high rate error-correction code, but with lessredundancy. Accordingly, puncturing may be effectively employed toreduce processing overhead at the decoder 708 in the receiver whenchannel conditions produce a relatively high signal to noise ratio.

A convolutional decoder 708 may be used to decode m-bit informationstrings from a bit stream that has been encoded using a convolutionalcode. The decoder 708 may comprise a Viterbi decoder, an algebraicdecoder, or another suitable decoder. In one example, a Viterbi decoderemploys the well-known Viterbi algorithm to find the most likelysequence of signaling states (the Viterbi path) that corresponds to areceived bit stream 724. The bit stream 724 may be decoded based on astatistical analysis of LLRs calculated for the bit stream 724. In oneexample, a Viterbi decoder may compare and select the correct Viterbipath that defines a sequence of signaling states using a likelihoodratio test to generate LLRs from the bit stream 724. Likelihood ratioscan be used to statistically compare the fit of a plurality of candidateViterbi paths using a likelihood ratio test that compares the logarithmof a likelihood ratio for each candidate Viterbi path (i.e. the LLR) todetermine which path is more likely to account for the sequence ofsymbols that produced the bit stream 724.

At the receiver, the same decoder used for decoding non-puncturedbitstreams can typically be used for decoding punctured bitstreams,regardless of how many bits have been punctured. In conventionalreceivers, the LLR information is typically de-punctured before decodingis attempted by filling LLRs for punctured states or positions(de-punctured LLRs) with zeros. A decoder may disregard de-puncturedLLRs that effectively carry no information.

Example Puncturing for Structured LDPC Codes

Structured low density parity check (LDPC) codes have been defined forcertain systems, such as LDPC code for Wi-Fi systems operating accordingto the 802.11 wireless standard (e.g., 802.11an and 802.11ac systems)for example. As described above, LDPC is one example of an error codingscheme that can be used to encode information bits. LDPC codes may bedesigned for a fixed code rate. To increase the coding rate, code wordsmay be punctured.

Puncturing is the act of removing bits from the code word to yield ashorter code word. Thus, punctured variable nodes correspond to codeword bits (e.g., information bits or systematic bits) that are notactually transmitted. Puncturing a variable node in a LDPC code createsa shortened code (e.g. due to the removal of a bit) and, thus, anincreased code rate can be achieved. For example, for a given LDPCmatrix, if the base transmitted block length is n−p, where p is thenumber of punctured columns (a column corresponding to a variable nodein the associated bipartite graph), n is the number of columns, and thenumber of base parity checks is m (e.g., corresponding to rows in thematrix and check nodes in the associated bipartite graph), then the coderate for the punctured LDPC code is (n−m)/(n−p). The binary informationblock size is (n−m)*Z, where Z is the lifting, and the transmitted blocksize is (n−p)*Z.

Techniques are provided herein for puncturing structured LDPC codes thatmay help achieve a desired code rate. For example, techniques hereinprovide for puncturing highest degree variable nodes of a 5/6 code rateWi-Fi LDPC code to produce a 7/8 code rate LDPC code. In some cases, thepuncturing is performed on starting bits of the code. Aspects hereinalso provide designs for rate 7/8 LDPC codes with enhanced performance.

According to certain aspects, high-degree (systematic) variables nodesof a structured LDPC code can be punctured, for example, to increase thecode rate. This may provide performance to capacity benefits. Puncturinga high-degree variable node can correspond to puncturing only a singlecolumn of a corresponding parity matrix—rather than puncturing randombits or multiple lower degree variable nodes.

Puncturing of a high-degree variable node (e.g., the highest degreevariable node) can be done such that each check node, which is connectedto a punctured variable node, is connected to only one such puncturedvariable node. In other words, the puncturing can be performed such thatfew or no check nodes are connected to multiple punctured variablenodes. For example, in a lifted LDPC code, the highest degree variablenode (e.g., the variable in the LDPC code structure that is connected tothe highest number of check nodes in the associated bipartite graph) canbe punctured (e.g., across the permutations).

If puncturing of the highest degree variable node does not provide thedesired code rate, other (e.g., additional) variable nodes can be usedfor puncturing such that the number of check nodes with more than twopunctured variable nodes is minimized (e.g., by puncturing anotherhighest-degree variable node or a variable node having the next highestdegree of connectivity to the check nodes).

Avoiding creation of check nodes that have multiple punctured variablenodes may help to ensure that the resulting punctured LDPC code containsa low number of check nodes that are “dead” at the start of decoding.Additionally, this type of puncturing pattern can avoid the formation ofsmall-size trapping sets (e.g., also referred to as loops) such as4-cycles, 6-cycles, etc.). A loop (or cycle) is defined as a closed pathwith no repeated nodes. This implies it has an even length. A cycle in aTanner (bipartite) graph refers to a finite set of connected edges. Theedge starts and ends at the same node, and it satisfies the conditionthat no node (except the initial and final node) appears more than once.The length of a cycle is simply the number of edges of the cycle.

Example 7/8 LDPC Code by Puncturing 5/6 Wi-Fi Code

According to certain aspects, one way to obtain an LDPC code withenhanced performance may be based on puncturing highest degree variablenodes of a Wi-Fi LPDC code. FIG. 8 illustrates example operations 800for wireless communication, in accordance with certain aspects of thepresent disclosure. Operations 800 may be performed, for example, by atransmitting device (e.g., UE 116 or BS 102). Operations 800 may begin,at 802, by encoding a set of information bits based on a LDPC code toproduce a code word (e.g., rate 5/6 code word), the LDPC code defined bya matrix having a first number of variable nodes and a second number ofcheck nodes. At 804, the transmitting device punctures the code word toproduce a punctured code word, wherein the puncturing is performedaccording to a first puncturing pattern designed to puncture bitscorresponding to one or more of the variable nodes having a certaindegree of connectivity to the check nodes (e.g., to achieve a code rateof 7/8 for the punctured code word). At 806, the transmitting devicetransmits the punctured code word.

For example, starting from a 5/6 rate Wi-Fi LDPC code (e.g., an 802.11acor 802.11an LDPC code), highest degree variable nodes can be puncturedto produce a 7/8 rate LDPC code. According to certain aspects, this maybe done by puncturing from the start of the 5/6 Wi-Fi LDPC code. In oneexample, the starting 93 bits of the 5/6 Wi-Fi LDPC code may bepunctured (corresponding to the highest degree variable node(s)). Inthis case, 81 bits may be punctured from the first column of the basegraph for the rate 5/6 Wi-Fi LDPC code corresponding to the highestdegree variable node, and the remaining 12 bits can be punctured fromthe second column of the base graph. This may be done to achieve around5% gains.

According to certain aspects, for puncturing greater than 5% (e.g., toobtain a code rate higher than 7/8), first bits can be punctured at thestart (e.g., from the highest degree variable node) and the remainingbits can be punctured periodically with a fixed periodicity (e.g., 20).

According to certain aspects, other puncturing patterns can be used. Forexample, tail puncturing (puncturing bits at the end), periodicpuncturing (e.g., puncturing from the start at a fixed periodicity),hybrid puncturing (e.g., puncturing half of the bits from the start at afixed periodicity and puncturing the other half of the bits at the end).

FIG. 9 shows a base graph representation of an exemplary 5/6 rate Wi-FiLDPC code 900. As shown in FIG. 9, the base graph includes 24 variablenodes 902 and 4 check nodes 904. As shown, the variable nodes havevarious degrees of connectivity to the check nodes.

The rate 5/6 Wi-Fi LDPC code 900 can be lifted Z=81 as a multi-edge typestructure and can have a density evolution gap (AWGN) to capacity of0.46 dB. If a parity column is punctured (e.g., at random) for a lowdegree node (e.g., 2 degree node 1002 as shown in FIG. 10) for a rate20/23 base graph the AWGN gap to capacity may be 0.49 dB. Puncturing ahighest degree variable node (e.g., 4 degree 1102 as shown in FIG. 11)may provide an AWGN gap to capacity of 0.39 dB. Thus, high-degreevariable node puncturing can provide a 0.1 dB improvement.

FIG. 12 is a graph 1200 showing performance of the various puncturingtechniques of an LDPC code at modulation and coding scheme (MCS) 9 with93 punctured bits and FIG. 13 is a graph 1300 showing performance of thevarious puncturing techniques of an LDPC code at MCS 1 with 100punctured bits, run 20 iterations, in accordance with certain aspects ofthe present disclosure. As shown in FIG. 12, for MCS 9 (e.g., 256 QAM),the curve 1202 shows performance for puncturing at the start showsbetter performance than the curves 1204, 1206, and 1208 for tailpuncturing, hybrid puncturing, and periodic puncturing, respectively. Asshown in FIG. 13, for MCS 1 (e.g., QPSK), the curve 1302 showsperformance for puncturing at the start shows better performance thanthe curves 1304, 1306, and 1308 for periodic puncturing, hybridpuncturing, and tail puncturing, respectively.

Example Rate 7/8 LDPC Code Design

Rate 7/8 LDPC codes obtained via puncturing of the rate 5/6 Wi-Fi LDPCcode can result in reducing the code blocklength of the code. In somecases, maintaining the blocklength (e.g., 1944 bits for lift size Z=81)may be desirable. According to certain aspects, multi-edge rate 7/8 LDPCcodes can be designed that are not based on puncturing of the rate 5/6Wi-Fi code. FIG. 14 illustrates example operations 1400 for wirelesscommunication, in accordance with certain aspects of the presentdisclosure. Operations 1400 may be performed, for example, by atransmitting device (e.g., UE 116 or BS 102). Operations 1400 may begin,at 1402, by encoding a set of information bits based on a multi-edgeLDPC code to produce a code word, the LDPC code defined by a matrixhaving a first number of variable nodes including an extra variablenode, relative to a reference LDPC code, and a second number of checknodes. At 1404, the transmitting device punctures the code word toproduce a punctured code word, wherein the puncturing is performedaccording to a puncturing pattern designed to puncture bitscorresponding to one or more of the variable nodes to achieve a certaincode rate (e.g., a 7/8 code rate) for the punctured code word. At 1406,the transmitting device transmits the punctured code word.

FIGS. 15-16 show a matrix representation of example multi-edge rate 7/8LDPC codes that maintain a blocklength of 1944 bits for lift size Z=81,in accordance with certain aspects of the present disclosure. The rate7/8 LDPC codes shown in FIGS. 15 and 16 have a threshold that is around0.08 dB better than the rate 7/8 Wi-Fi LDPC code.

In the definition of standard irregular LDPC code ensembles (degreedistributions), all edges in the Tanner graph representation may bestatistically interchangeable. In other words, there exists a singlestatistical equivalence class of edges. For multi-edge LDPC codes,multiple equivalence classes of edges may be possible. While in thestandard irregular LDPC ensemble definition, nodes in the graph (bothvariable and constraint) are specified by their degree, i.e., the numberof edges they are connected to, in the multi-edge type setting an edgedegree is a vector; it specifies the number of edges connected to thenode from each edge equivalence class (type) independently.

A multi-edge type ensemble is comprised of a finite number of edgetypes. The degree type of a constraint node is vector of (non-negative)integers; the i-th entry of this vector records the number of sockets ofthe i-th type connected to such a node. This vector may be referred toas an edge degree. The degree type of a variable node has two partsalthough it can be viewed as a vector of (non-negative) integers. Thefirst part relates to the received distribution and will be termed thereceived degree and the second part specifies the edge degree. The edgedegree plays the same role as for constraint nodes. Edges are typed asthey pair sockets of the same type. This constraint, that sockets mustpair with sockets of like type, characterizes the multi-edge typeconcept. In a multi-edge type description, different node types can havedifferent received distributions (e.g., the associated bits may gothrough different channels).

In the matrix representations shown in FIGS. 15 and 16, there are 4edge-types and the vector d denotes the edge-type vector, the vectorb=(1,0) denotes the punctured node, the vector vb,d denotes the variablenode degree, the vector vb,dn denotes the number of variable nodes ofthat degree, the vector ud denotes the check node degree, and the vectorudn denotes the number of check node of that degree.

The LDPC codes shown in FIGS. 15 and 16 introduce a high-degreepunctured variable node (e.g., an extra code bit) in the base graph(e.g., for a total of 25 variable nodes in the base graph—rather thanthe 24 shown in FIG. 9). The additional punctured variable node is ofthe highest degree in both the constructions and provides a degree offreedom in constructing a better high rate (7/8) code. Thus, the numberof columns in the base parity-check matrix is 25. The number of checknodes in the base matrix are 4. For lift size 81, if the high-degreevariable node is punctured, the remaining nodes are 24×81=1944,therefore, maintaining the 1944 blocklength.

Example Puncturing for Retransmission

According to certain aspects, puncturing bits can be different (e.g.,switched) for retransmissions. For subsequent retransmissions ofinformation, the puncturing bits can be switched among nodes of the sameor similar degree. For example, for the first transmission, 93 bits canbe punctured from the start (e.g., bits [0-92]), while for the secondtransmission, puncturing can be performed at an offset (e.g., at anoffset of 10, bits [10-112] might be punctured).

The methods disclosed herein comprise one or more steps or actions forachieving the described method. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

In some cases, rather than actually transmitting a frame, a device mayhave an interface to output a frame for transmission. For example, aprocessor may output a frame, via a bus interface, to an RF front endfor transmission. Similarly, rather than actually receiving a frame, adevice may have an interface to obtain a frame received from anotherdevice. For example, a processor may obtain (or receive) a frame, via abus interface, from an RF front end for transmission.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

For example, means for encoding may include one or more processors, suchas the TX data processor 214, TX MIMO processor 220, and/or theprocessor 270 of the wireless base station 210 illustrated in FIG. 2;the TX data processor 238, Modulator 280, and/or the processor 270 ofthe wireless node 250 illustrated in FIG. 2; the transmitter 310, theDSP 320, and/or the processor 304 of the wireless device 302 illustratedin FIG. 3; and/or the encoder 602 of the encoder 600 illustrated in FIG.6. Means for puncturing may comprise a processing system, which mayinclude one or more processors, such as the TX data processor 214, TXMIMO processor 220, and/or the processor 270 of the wireless basestation 210 illustrated in FIG. 2; the TX data processor 238, Modulator280, and/or the processor 270 of the wireless node 250 illustrated inFIG. 2; the transmitter 310, the DSP 320, and/or the processor 304 ofthe wireless device 302 illustrated in FIG. 3; and/or the puncturingmodule 604 of the encoder 600 illustrated in FIG. 6. Means fortransmitting comprise a transmitter, which may include the TX dataprocessor 214, TX MIMO processor 220, the transceiver(s) 222 a-222 t,and/or the antenna(s) 224 a-224 t of the wireless base station 210illustrated in FIG. 2; the TX data processor 238, the modulator 280, thetransceiver(s) 252 a-252 r, and/or the antenna(s) 252 a-252 r of thewireless node 250 illustrated in FIG. 2; the transmitter 310 and/or theantenna(s) 316 of the wireless device 302 illustrated in FIG. 3; and/orthe TX chain 608 and antenna 610 of the encoder 600 illustrated in FIG.6.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

If implemented in hardware, an example hardware configuration maycomprise a processing system in a wireless node. The processing systemmay be implemented with a bus architecture. The bus may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system and the overall design constraints.The bus may link together various circuits including a processor,machine-readable media, and a bus interface. The bus interface may beused to connect a network adapter, among other things, to the processingsystem via the bus. The network adapter may be used to implement thesignal processing functions of the PHY layer. In the case of a wirelessnode (see FIG. 1), a user interface (e.g., keypad, display, mouse,joystick, etc.) may also be connected to the bus. The bus may also linkvarious other circuits such as timing sources, peripherals, voltageregulators, power management circuits, and the like, which are wellknown in the art, and therefore, will not be described any further. Theprocessor may be implemented with one or more general-purpose and/orspecial-purpose processors. Examples include microprocessors,microcontrollers, DSP processors, and other circuitry that can executesoftware. Those skilled in the art will recognize how best to implementthe described functionality for the processing system depending on theparticular application and the overall design constraints imposed on theoverall system.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer-readable medium.Software shall be construed broadly to mean instructions, data, or anycombination thereof, whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. The processor may beresponsible for managing the bus and general processing, including theexecution of software modules stored on the machine-readable storagemedia. A computer-readable storage medium may be coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a wireless node and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a wirelessnode and/or base station can obtain the various methods upon coupling orproviding the storage means to the device. Moreover, any other suitabletechnique for providing the methods and techniques described herein to adevice can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

What is claimed is:
 1. A method for wirelessly transmitting data inaccordance with a radio technology, comprising: encoding, by encodercircuity, a set of information bits based on a low density parity check(LDPC) code to produce a code word, the LDPC code defined by a basegraph having a first number of variable nodes and a second number ofcheck nodes; puncturing, by puncturing circuitry, bits of the code wordcorresponding to at least the variable node of the first number ofvariable nodes at a start of the code word having a highest degree ofconnectivity to the second number of check nodes and one or more bits atan end of the code word to produce a punctured code word; andtransmitting, via transmitting circuitry, the punctured code word inaccordance with the radio technology across a wireless channel.
 2. Themethod of claim 1, further comprising puncturing, by the puncturingcircuitry, remaining bits of the code word, excluding the bitscorresponding to the at least one variable node at the start of the codeword, with a periodicity.
 3. The method of claim 1, wherein thepuncturing comprises puncturing such that a number of the check nodes inthe punctured code word that are connected to more than one variablenode having punctured bits is minimized.
 4. The method of claim 1,wherein the puncturing comprises puncturing such that a number of closedloops in the punctured code word is minimized.
 5. The method of claim 1,wherein the puncturing remaining bits of the code word, excluding theone or more bits at the end of the code word, with a periodicity.
 6. Themethod of claim 1, further comprising: for a retransmission of the setof information bits, puncturing different bits of a code word for theset of retransmitted information bits.
 7. The method of claim 6, whereinthe puncturing comprises puncturing bits in the code word for the set ofretransmitted information bits corresponding to different variable nodesthan the at least one variable node, wherein the different variablenodes have a same degree of connectivity to check nodes as the at leastone variable node.
 8. The method of claim 6, wherein the puncturingcomprises puncturing bits in the code word for the set of retransmittedinformation bits at a defined offset relative to the bits in thepunctured code word.
 9. The method of claim 1, wherein the LDPC codecomprises an 802.11 Wi-Fi LDPC code.
 10. The method of claim 1, whereinthe code word is associated with a code rate of 5/6 and the puncturedcode word is associated with a code rate of 7/8.
 11. A method forwirelessly transmitting data in accordance with a radio technology,comprising: encoding, via encoding circuitry, a set of information bitsbased on a multi-edge low density parity check (LDPC) code to produce acode word, the LDPC code defined by a base graph having a first numberof variable nodes including an extra variable node, relative to a 802.11wireless local area network (WLAN) LDPC code, and a second number ofcheck nodes; puncturing, via puncturing circuitry, bits of the code wordcorresponding to one or more of the first number of variable nodes toproduce a punctured code word associated with a code rate of 7/8; andtransmitting, via transmitting circuitry, the punctured code word inaccordance with the radio technology across a wireless channel.
 12. Themethod of claim 11, wherein the one or more variable nodes includes theextra variable node.
 13. The method of claim 11, wherein the puncturedcode word has a same block length as the reference 802.11 WLAN LDPCcode.
 14. The method of claim 11, wherein the LDPC code has a liftingvalue of 81 and the punctured code word has a block length of 1944 bits.15. An apparatus for wirelessly transmitting data in accordance with aradio technology, comprising: means for encoding a set of informationbits based on a low density parity check (LDPC) code to produce a codeword, the LDPC code defined by a base graph having a first number ofvariable nodes and a second number of check nodes; means for puncturingbits of the code word corresponding to at least the variable node of thefirst number of variable nodes at a start of the code word having ahighest degree of connectivity to the second number of check nodes andone or more bits at an end of the code word to produce a punctured codeword; and means for transmitting the punctured code word in accordancewith the radio technology across a wireless channel.
 16. The apparatusof claim 15, wherein the means for puncturing is configured to punctureremaining bits of the code word, excluding the bits corresponding to theat least one variable node at the start of the code word, with aperiodicity.
 17. The apparatus of claim 15, wherein the means forpuncturing is configured to puncture the code word such that a number ofthe check nodes in the punctured code word that are connected to morethan one variable node having punctured bits is minimized.
 18. Theapparatus of claim 15, wherein the means for puncturing is configured topuncture the code word such that a number of closed loops in thepunctured code word is minimized.
 19. The apparatus of claim 15, whereinthe means for puncturing is configured to puncture remaining bits of thecode word, excluding the one or more bits at the end of the code word,with a periodicity.
 20. The apparatus of claim 15, wherein the means forpuncturing is further configured to: for a retransmission of the set ofinformation bits, puncture different bits of a code word for the set ofretransmitted information bits.
 21. The apparatus of claim 20, whereinthe means for puncturing is configured to puncture bits in the code wordfor the set of retransmitted information bits corresponding to differentvariable nodes than the at least one variable node, wherein thedifferent variable nodes have a same degree of connectivity to checknodes as the at least one variable node.
 22. The apparatus of claim 20,wherein the means for puncturing is configured to puncture bits in thecode word for the set of retransmitted information bits at a definedoffset relative to the bits in the punctured code word.
 23. Theapparatus of claim 15, wherein the LDPC code comprises an 802.11 Wi-FiLDPC code.
 24. The apparatus of claim 15, wherein the code word isassociated with a code rate of 5/6 and the punctured code word isassociated with a code rate of 7/8.
 25. An apparatus for wirelesslytransmitting data in accordance with a radio technology, comprising:means for encoding a set of information bits based on a multi-edge lowdensity parity check (LDPC) code to produce a code word, the LDPC codedefined by a base graph having a first number of variable nodesincluding an extra variable node, relative to a 802.11 wireless localarea network (WLAN) LDPC code, and a second number of check nodes; meansfor puncturing bits of the code word corresponding to one or more of thefirst number of variable nodes to produce a punctured code wordassociated with a code rate of 7/8; and means for transmitting thepunctured code word in accordance with the radio technology across awireless channel.
 26. The apparatus of claim 25, wherein the one or morevariable nodes includes the extra variable node.
 27. The apparatus ofclaim 25, wherein the punctured code word has a same block length as the802.11 WLAN LDPC code.
 28. The apparatus of claim 25, wherein the LDPCcode has a lifting value of 81 and the punctured code word has a blocklength of 1944 bits.
 29. An apparatus for wirelessly transmitting datain accordance with a radio technology, comprising: encoding circuitryconfigured to encode a set of information bits based on a low densityparity check (LDPC) code to produce a code word, the LDPC code definedby a base graph having a first number of variable nodes and a secondnumber of check nodes; puncturing circuitry configured to puncture bitsof the code word corresponding to at least the variable node of thefirst number of variable nodes at a start of the code word having ahighest degree of connectivity to the second number of check nodes andone or more bits at an end of the code word to produce a punctured codeword; and transmitting circuitry configured to transmit the puncturedcode word in accordance with the radio technology across a wirelesschannel.
 30. An apparatus for wirelessly transmitting data in accordancewith a radio technology, comprising: encoding circuitry configured toencode a set of information bits based on a multi-edge low densityparity check (LDPC) code to produce a code word, the LDPC code definedby a base graph having a first number of variable nodes including anextra variable node, relative to a 802.11 wireless local area network(WLAN) LDPC code, and a second number of check nodes; puncturingcircuitry configured to puncture bits of the code word corresponding toone or more of the first number of variable nodes to produce a puncturedcode word associated with a code rate of 7/8; and transmitting circuitryconfigured to transmit the punctured code word in accordance with theradio technology across a wireless channel.
 31. A non-transitorycomputer readable medium having computer executable code stored thereon,comprising: code for encoding a set of information bits based on a lowdensity parity check (LDPC) code to produce a code word, the LDPC codedefined by a base graph having a first number of variable nodes and asecond number of check nodes; code for puncturing bits of the code wordcorresponding to at least the variable node of the first number ofvariable nodes at a start of the code word having a highest degree ofconnectivity to the second number of check nodes and one or more bits atan end of the code word to produce a punctured code word; and code fortransmitting the punctured code word in accordance with a radiotechnology across a wireless channel.
 32. A non-transitory computerreadable medium having computer executable code stored thereon,comprising: code for encoding a set of information bits based on amulti-edge low density parity check (LDPC) code to produce a code word,the LDPC code defined by a base graph having a first number of variablenodes including an extra variable node, relative to a 802.11 wirelesslocal area network (WLAN) LDPC code, and a second number of check nodes;code for puncturing bits of the code word corresponding to one or moreof the first number of variable nodes to produce a punctured code wordassociated with a code rate of 7/8; and code for transmitting thepunctured code word in accordance with a radio technology across awireless channel.
 33. A method for wireless communication by atransmitting device, comprising: encoding, by an encoder of a radiofrequency (RF) modem, a set of information bits based on a low densityparity check (LDPC) code to produce a code word, the LDPC code definedby a base graph having a first number of variable nodes and a secondnumber of check nodes; puncturing, by a puncturing module of the RFmodem, bits of the code word corresponding to at least one of the firstnumber of variable nodes at a start of the code word having a highestdegree of connectivity to the second number of check nodes a number ofbits at an end of the code word to produce a punctured code word; andtransmitting, via one or more antennas of a transmitter, the puncturedcode word.